1. Field of the Invention
The present invention relates generally to couplings for concentric shafts and, more particularly, to a concentric shaft coupling which incorporates a compliant member in conjunction with a spline arrangement as a component of each of two rotatable members, wherein the rotatable members are disposed in generally coaxial relation with each other.
2. Description of the Related Art
Concentric shafts are well known to those skilled in the art. For example, U.S. Pat. No. 2,727,485, which issued to Combs on Dec. 20, 1955, teaches the use of counter rotating shafts for a device which is used to transport freight over bodies of water. The submarine type sea train disclosed in this patent incorporates shafts which are arranged in both concentric and coaxial relation with each other along the length of a submarine for purposes of providing driving torque for the propellers of the vehicle.
U.S. Pat. No. 2,285,592, which issued to Ledwinka on June 9, 1942, discloses the use of counter rotating shafts that are arranged in concentric and coaxial relation with each other and are used to provide a driving force for a dual propeller system. The dual propellers are arranged to rotate about a common axis and are disposed proximate one another to neutralize the reaction torque of one propeller by the reverse rotation of the other propeller. Each of the propellers are driven by an internal gear with one q-ear being driven directly and the other gear being driven indirectly through an idler pinion.
U.S. Pat. No. 4,012,923, which issued to Lundgren on Mar. 22, 1977, discloses a vibration damping coupling which utilizes an elastomeric material. The device is used to transmit torque between at least two rotatable members. Each of the members have complimentary peripheral surface portions of non-circular cross-section with coupling members that comprise elastomer and metal layers disposed radially between driving and driven components. Each of the layers is disposed around a centerline with a generally hexagonal cross-section being described by each of the layers of both the elastomer and metal members.
U.S. Pat. No. 2,154,077, which issued to Sampson on Apr. 11, 1939, discloses the use of a compliant member disposed rad.:ally between an outer surface of one shaft and an inner surface of an associated shaft. The compliant member provides a drive coupling which is used as a universal joint to transmit torque between the coupled components. By yielding under stress, the compliant member accommodates misalignment and relative axial and angular displacement between the driving shaft and the driven shaft.
U.S. Pat. No. 4,516,956, which issued to Staiert on May 14, 1985, discloses a device which utilizes a compliant member to transmit torque between a driving shaft and a driven shaft. It also discloses a weld joint structure for use in assembling the elastomeric flexible coupling. Although this patent teaches the use of a spline connection between two of its components, the spline connection does not provide a back-up torque transmitting device for use when the compliant member deforms or fails.
U.S. Pat. No. 4,406,640, which issued to Franklin et al, on Sept. 27, 1983, discloses a drive axle assembly having a limited torsional damper. This axle assembly incorporates rubber bushings which are compressed between a shell and a canister. The drive axle assembly disclosed in this patent comprises a drive shaft with an integral flange at one end and a second drive shaft with an integral hollow head at an end adjacent the flange. The flange and head have cooperating lugs forming a lost motion positive drive assembly between the shafts. The assembly also includes a limited torsional damper comprising a shell welded to the flange, a canister welded to the head and a pair of rubber bushings compressed between the shell and the canister. Although this patent discloses the use of teeth which operate in a lost motion manner as a back up device for the rubber bushings, the rubber bushings and the lost motion device are displaced axially in a manner which would prevent the device from exhibiting the articulation ability that is sometimes necessary to accommodate misalignment of the input and output shafts. Furthermore, the lost motion lugs described in this patent do not transmit torque unless a failure occurs in the rubber bushing component and therefore are not arranged to normally share torque when the torque between the driving and driven members exceeds a predetermined magnitude.
Copending patent application Ser. No. 071,446, teaches the use of an elastomeric component in conjunction with a spline arrangement for the purpose of transmitting torque between a driving member and a driven member wherein the elastomeric, or compliant, component transmits the torque when the magnitude of the torque is less than a predefined value and, when the torque is greater than the predetermined magnitude, the torque transmission is shared between the compliant member and a spline arrangement.